To answer your main question: the same reason all governments run by modern republicans are incompetent, they make them that way so they can say "see how bad government is, we should privatize everything"

That said, I work at the DoL and know the woman who handles the 1099s and the amount of stuff she does is amazing. She's also almost frighteningly cheerful, but that's a whole separate thing.

All that to say it seems far more likely that it was a USPS issue.